you shouldn't undo your extreme act of kindness by bitterness and mean spiritedness.
you should have known about women like these. they are often gypsies. you see them all the time in london. they hang out before friday prayer near regent's park mosque. some are muslims, some not, (i guess).
you should know that there are many, many Albanian women in the sex trade -- women who either sell themselves or beg on the street. it is bitter reality that everybody knows about.
most likely though she is part of a romanian or albanian caravan, and they go from city to city either robbing people or begging. but other than that they are harmless, and back home they are reallllllly, reallllllly treated badly.
when you give money to someone as zakah, or charity -- the intention should be to do something right. if it helps them then great, but if they scam you, well,....,who really cares, you did the right thing. and doing the right thing betters society and purifies you and your wealth.
there is a prophetic story i am sure you know -- a man gave charity to a woman begging on the street. when his friends/family found out, they lambasted him. she was a prostitute! how could he give money to such a lowlife, they screamed. but that money helped turn the woman away from prostitution. has there ever been money better spent?!
anyhow, as muslims we are supposed to give and give, and give some more to such an extent that the left hand doesn't know what the right is doing. (the left metaphorically prevents the right from giving). whether that money is wasted or used wisely is not our problem. our responsibility is only to give as much we can.
one final thing, you should not be bitter about somebody much poorer than you cheating you or taking advantage of you. you will recall that one the people who most vigorously spread rumours of Aisha's (ra) alleged infidelity was a relative of Abu Bakr. when Abu Bakr (ra) found out, he became very upset. it turns out that Abu Bakr (ra) had been regularly giving charity to that relative. however, after this betrayal, he angrily stopped, feeling cheated and taken advantage of, albeit by someone very, very poor.
what happened next? something amazing. abu bakr was rebuked by none other than a new revelation in the quran. he was told to be less tight-minded toward his destitute relative (who had since acknowledged his idiocy) and told to resume his charity.
in anycase, you have done a wonderful thing, although something outrageously naive. don't be upset. worse things have happened. (for example i once gave money to a woman to buy a piece of land. little did idiot me know that this would erupt in a family feud and her murder by her husband).
frankly speaking, i am only writing this post, so the message gets through to myself. i live in a muslim country. everyday, on every street corner i see women and street children begging. after friday prayer the beggars just swarm you. however, as in most muslim countries, people here are very, very, very, very, very, very hardhearted. they just tell beggers to get lost or bugger off. get a job!, they scream. such poverty would not be tolerated in non-muslim countries, but here muslims are just too small minded to give a damn. maybe that's why allah has kept these small minded muslim countries very small indeed....